Scale the fish by placing it in the sink under cold running water. Grasp fish firmly by the gills and scrape off scales with a fish scaler or small, dull knife. Using short strokes, work from the tail to the head.
To remove the head, cut the flesh on both sides with a knife. If the fish is small, slice directly through the spine. For a larger fish, place knife between vertebrae and tap the back of the knife with a hammer.
To bone and butterfly, remove belly fins with scissors and slice off the dorsal and anal fins. Slit open belly cavity and use scissors to cut through ribs on both sides of the backbone. Using a sharp knife, scrape flesh away from the backbone. Slide knife under rib bones and lift them off. Check to make sure all no tiny rib bones remain.
Before cooking, always remove the dark flesh lying directly below the lateral line. The lateral line is a string of tiny holes with nerve connections sensitive to vibrations in the water. It is often visible as a dark line running along both sides of the fish.
The secret to successful mullet cookery is to not overcook. Whichever of the following cooking methods you choose, your mullet will be cooked when its flesh becomes opaque, but is still moist and can easily be pierced with a fork.
Place mullet in a greased baking dish, or wrap in oiled foil and place on a baking sheet. Brush with melted butter or oil and season with salt and pepper, or cover with a sauce. Bake in a preheated 450°F (230°C) oven.
Place whole small fish directly on a greased grill, 4 to 6 inches (about 10 to 15cm) above prepared coals or fire. Baste with butter, oil, or marinade and close hood of grill. Cook until fish is opaque and moist on the inside, about 6 to 8 minutes.
Coat mullet with seasoned flour, crumbs, or cornmeal. Shake off any extra coating and fry in a small amount of hot butter or oil, turning once halfway through cooking time. Cook until opaque and moist on the inside, about 4 to 8 minutes.
Bring poaching liquid, consisting of water, broth, and herbs and spices, to a simmer. Slip in the mullet, then cover pan and keep liquid at a simmer for about 8 minutes per inch (about 2.45cm) of thickness.
Place mullet on a perforated rack over 1 to 2 inches (about 2.5 to 5cm) of rapidly boiling water. Cover with a tight-fitting lid and keep water at a constant boil through cooking time, about 8 minutes for each inch (about 2.5cm) of thickness.